This invention relates to a compressor oil composition having excellent oxidation stability.
Compressor oils are generally used in compressors for their action of cooling by removing the heat generated by adiabatic compression, action of lubricating bearing and other parts, and action of sealing to prevent gas leakage at sliding parts. Gases to be compressed include, for example, air, oxygen, carbon dioxide, nitrogen, hydrogen, hydrocarbons, chlorine, and ammonia. Air compressors are used most frequently, and impose the most severe oxidizing conditions on compressor oils.
Within the air compressors, the most severe oxidizing conditions for compressor oils are set up owing to the presence of high-temperature high-pressure air, the presence of metals performing a catalytic action on oxidation such as copper or iron, and the presence of condensed water generated by compression, etc. For this reason, when an ordinary turbine oil, engine oil, or hydraulic actuating oil, etc. is used as the compressor oil, the oil is oxidatively deteriorated within very short periods of time, and at the same time, serious troubles such as the formation of sludge or the corrosion of a copper-containing material are caused. Once such a phenomenon has occurred, the original state cannot be restored unless the compressor is overhauled or cleaned completely. The cost and time required for this procedure would be enormous.
A great number of compounds such as aromatic amines, alkylphenols, zinc dialkyldithiophosphates or zinc dithiocarbamate have been known and commercially used as antioxidants to be added to lubricating oils. However, when such a compound is used alone in mineral lubricating oils for compressors, the oils are oxidatively deteriorated within short periods of time and become useless.
Combinations of these antioxidant compounds are also disclosed, for example, in Japanese Patent Publication No. 17615/61, Japanese Laid-Open Patent Publication No. 91462/73, U.S. Pat. No. 2,739,122, and DAS 1,594,405, but have not proved entirely satisfactory.
It is an object of this invention therefore to provide a lubricating oil composition for compressors having excellent oxidation stability, which has a much longer life under oxidation conditions than in the case of using conventional antioxidants for compressor oils, and which even when oxidatively deteriorated, is scarcely likely to cause serious troubles such as the formation of sludge.